Electric motor

ABSTRACT

An electric motor comprising a rotor and a stator is disclosed. The rotor is supported on a substantially spherical bearing and is of a substantially spherical design facing the stator, which has a high degree of efficiency. The stator may have a magnetic return-path body which is made of a compressed powder material. The return-path body may be of a substantially spherical design, at least in segments facing the rotor.

RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.11/125,536, filed May 9, 2005, which is a Continuation of U.S.application Ser. No. 10/648,846, filed Aug. 25, 2003, which relates tothe subject matter disclosed in German patent application No. 102 51647.2 of Oct. 30, 2002, each of which are incorporated herein byreference in their entirety and for all purposes.

FIELD OF THE INVENTION

The invention relates to an electric motor comprising a rotor and astator. In particular, the invention relates to motors wherein the rotormay be supported on a substantially spherical bearing and is of asubstantially spherical design facing the stator.

Electric motors of this type are used, in particular, in the case ofcentrifugal pumps. They have the advantage that mounting of the rotorfree of play may be achieved. Such electric motors are described, forexample, in DE 33 02 349 A1 or DE 15 38 717.

SUMMARY OF THE INVENTION

In accordance with embodiments of the present invention, an electricmotor which has a high degree of efficiency is provided.

This is accomplished in accordance with certain embodiments of theinvention in that the stator has a magnetic return-path body which ismade of a compressed powder material and that the return-path body is ofa substantially spherical design facing the rotor, at least in segmentsfacing the rotor.

The production of the return-path body from a compressed powder materialresults in a high variability with respect to the shaping for thereturn-path body. This can be optimized as a result in order to ensure ahigh transfer of magnetic flux to the rotor with minimal losses. Athree-dimensional, optimized shaping may, in particular, be achieved.

In the case of known powder materials, such as SOMALOY of the companyHoganas AB, Sweden (SOMALOY is a registered trademark), iron granulesand, in particular, soft-magnetic iron granules are insulatedelectrically in relation to one another. Only slight eddy-current lossesthen occur in a return-path body while the required magnetic propertiesare present. Simultaneously with the optimal, functional properties(large magnetic conductivity, small electric conductivity), an optimalgeometric shape of the return-path body may also be produced.

When the return-path body is of a substantially spherical design, forexample, at least in segments facing the rotor, a spheroid motor may berealized with a small air gap which is, in particular, essentially inthe shape of a substantially spherical shell. In the case of a small airgap, the magnetic transfer from the stator to the rotor can be optimal.

The coupling of the magnetic field into the return-path body by way ofcoils on the return-path body can also be optimized via the manufactureof the return-path body by a compressed powder material. It is possiblefor that part of the return-path body which is located in the area ofthe part of the coil generating the magnetic field to have a crosssection which is sufficient (and, in particular, just sufficient) totransport magnetic flux without oversaturation, while the areatransferring magnetic flux to the rotor may have a large surface.Altogether, a high degree of efficiency may be achieved as a result, andthe material required for windings can be minimized.

It is desirable that the return-path body be a compact body or havecompact return-path body elements. The return-path body can, in thisrespect, be in one part and, in particular, in one piece or be composedof several parts. As a result, a simple assembly may be realized. Inaddition, an optimal coupling-in of the magnetic field can result.

In one embodiment, the return-path body is composed, of a plurality ofreturn-path body elements, wherein these can be separate elements orelements interconnected in one piece. The return-path body elements maybe optimized in order to achieve a high degree of efficiency for theelectric motor.

A return-path body may be manufactured in the case of separatereturn-path body elements in that adjacent return-path body elements maybe connected via a plug connection. A return-path body may then bemanufactured in a simple and quick manner, wherein coil-receivingportions of different types may be manufactured depending on the use.

One embodiment of the return-path body comprises, a plurality ofsegments, each segment having a substantially spherical surface facingthe rotor. For example, the envelope of the surface may be part of aspherical surface. Such a return-path body may be produced in a simplemanner and optimized with respect to its shaping such that a high degreeof electrical efficiency is achieved with a minimized use of materialwith respect to coil windings. A segment can, in this respect, be formedin one piece on a return-path body or be formed on a return-path bodyelement, wherein several return-path body elements then form thereturn-path body.

In a variation of one embodiment, adjacent segments are separatedmagnetically in that a gap may be formed between such adjacent elements.In this way, a multipolar stator arrangement can be realized. In otherembodiments, it may be provided for the return-path body to have acomplete spherical surface, wherein the magnetic separation is thenbrought about via electric separation of adjacent coils.

It is then provided, in particular, for segments to be connected to oneanother via a return-path area, wherein the return-path area can connectadjacent segments to one another or can connect oppositely locatedsegments to one another in order to provide the magnetic return path inthis way.

In particular, the return-path body surrounds the rotor in a ring shape,wherein the return-path body can have a complete surface or a pluralityof substantially spherical surfaces with a substantially sphericalenvelope, depending on the use.

It may be desirable that the powder material comprises iron granulesand, in particular, soft iron granules which are insulated electricallyrelative to one another. Such a powder material is available under thename SOMALOY™ from the Hoganas company, Sweden. While the magneticproperties are optimized, eddy current losses in the electric motor canbe minimized so a high degree of efficiency can be achieved.

It is particularly advantageous when the return-path body has at leastone coil receiving portion in order to accommodate windings for thestator.

It is then intended for the coil receiving portions to be provided withan electric insulation and/or for an accommodated coil to be providedwith an electric insulation towards the coil receiving portions. Theelectric insulation may be made, for example, by means of an insulatinglayer on the coil receiving portions or with a sheathing of theaccommodated coil. The electric insulation can also be formed by acorresponding insulating sleeve which is seated on the coil receivingportions, wherein the coil is then seated on the insulating sleeve.

It is particularly favorable when the at least one coil receivingportion is arranged and designed such that accommodated coils do notproject beyond the spherical area of the return-path body in thedirection of the rotor. As a result, the width of the air gap betweenthe rotor and the return-path body can be optimized so that an optimumtransfer of magnetic flux to the rotor is ensured. In the case of acirculation pump, for example, with which an electric motor inaccordance with an embodiment of the invention is used, the air gap canthen be dimensioned such that no significant frictional braking occurs.

In this respect, an air gap which is formed between the rotor and thespherical area of the return-path body can be, in particular, free fromcoils and so the spherical surface of the stator is determined solely bythe return-path body and not by coils seated on the return-path body.

Coil receiving portions can be formed in a simple manner from the pointof view of production engineering when the return-path body has aplurality of recesses as coil receiving portions or for the formation ofcoil receiving portions. Coils may then be inserted into such recessesor they may be wound into such recesses.

In this respect, a recess which has an area facing the rotor isfavorably set back in relation to the spherical surface of thereturn-path body. As a result, an area is made available which canaccommodate a coil at least partially without the coil itself projectingbeyond the spherical surface area of the return-path body.

It may be provided for a coil to be wound onto a coil receiving portion,in particular, when the return-path body is designed in one piece.

It may, however, also be provided for a prefabricated coil to be pushedonto or placed on a coil receiving portion. This is possible, inparticular, when the return-path body is composed of separatereturn-path body elements.

In addition, it is particularly favorable when a coil receiving portionis dimensioned such that the part of the return-path body which islocated in the area of the generated magnetic field of the accommodatedcoil is considerably smaller than the area of the return-path body whichtransfers the generated magnetic field to the rotor. As a result, themagnetic losses in the return-path body may be minimized and thetransfer of magnetic flux to the rotor optimized. Altogether, a highdegree of electric efficiency can be achieved as a result for theelectric motor in accordance with the invention.

It is particularly favorable when the coil receiving portion isdimensioned such that an adequate area of the return-path body is madeavailable in order to transport magnetic flux below the saturationlevel. As a result, magnetic losses can be kept low and, therefore, thedegree of electric efficiency is maximized. On the other hand, it ispossible via the spherical surface or spherical surfaces of thereturn-path body for magnetic flux to be transportable to the rotor overa maximum surface area. An optimum ratio of the surface areas withrespect to the transition of air of the return-path body and thetransition of the magnetic field to the coil receiving portion may thenbe made available. In the case of an AC motor, the ratio of thecorresponding surface areas is, for example, approximately 2.5:1 with acompressed powder return-path body consisting of SOMALOY. (This ratio isdependent on the material.)

A coil receiving portion is favorably designed such that a coil with around or approximately round cross section can be accommodated. In thecase of a round cross section, the winding portion of the coil (with apredetermined cross section) is minimized. As a result of the inventivesolution, coil geometries can be used, with which the ratio between thetransverse diameters is closer to one. (In the ideal case, with a coilwith a round cross section, the ratio is at one.)

Depending on the number of poles, the return-path body preferably has aplurality of spaced recesses as coil receiving portions which are setback in relation to the spherical surface.

In this respect, the recesses are, in particular, distributed uniformlyaround an inner circumference of the return-path body in order to makesymmetric ratios available in this way.

In one embodiment, a coil axis of a coil seated in the coil receivingportion lies substantially in circumferential direction of thereturn-path body, wherein the coil axis may be straight so that the coilaxis is seated substantially parallel to the tangential direction. Thecoil axis can also be curved and, in particular, correspond to acircumferential section of a circle.

In an alternative embodiment, a coil axis of a coil seated in the coilreceiving portion is aligned substantially radially.

When the return-path body has recesses which face the rotor, thereturn-path body may be designed with a small axial height and thevertical dimensions of the electric motor may be kept small. Thetransverse dimensions may likewise be kept small. It may, however, alsobe provided for the at least one coil receiving portion to be arrangedbehind or beneath the spherical surface area of the return-path bodyfacing the rotor in order to, for example, make a complete sphericalsurface available.

It may also be provided for the return-path body to have a connectingarea which is located transversely to an axis of rotation of the rotorand makes a transverse magnetic connection available in order tooptimize the return path in this way.

This connecting area can also be used for forming the at least one coilreceiving portion.

The design of the return-path body in accordance with the invention maybe realized with a large number of rotor configurations. In the case ofthe rotor, this may, for example, be a cage rotor, a rotor generating amagnetic field (synchronous rotor) or a hysteresis rotor. In the case ofthe electric motor itself, this may be an AC electric motor or a DCelectric motor.

In one embodiment, several coils are arranged on the return-path body astorus-shaped coils. These follow the contour of the return-path body inorder to project as little as possible into the air gap and to obtain anair gap with a minimum width in the case of a spherical surface of thereturn-path body. With this embodiment, some of the windings of the coilmay be arranged in the air gap, wherein this portion is, however,minimal.

As a result of the fact that the coils are of a torus-shaped design and,in particular, also follow the contour of the return-path body at itsside facing the rotor, a minimized portion of the surface area of thecoils is arranged in the air gap. With this embodiment, the return-pathbody, which can, in particular, be designed in one piece, forms as awhole a coil receiving portion for a plurality of coils. Adjacent coilsare separated electrically from one another. The number of coils isrelated to the number of poles.

A winding axis may be substantially parallel to a circumferentialdirection of the return-path body and may coincide with it. The windingaxis is, in this respect, curved.

The invention relates, in addition, to a circulation pump which isprovided with an electric motor.

This circulation pump has the advantages already explained inconjunction with the electric motor.

In this respect, a partition wall is, in particular, arranged in an airgap between rotor and return-path body. This partition wall separatesthe wet area from the return-path body. The width of the air gap may beadjusted by means of the inventive return-path body such that the airgap can still be selected, even with a partition wall, to be of such awidth that minimal frictional braking occurs but a high transport ofmagnetic flux towards the rotor is ensured.

The following description of preferred embodiments serves to explain theinvention in greater detail in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective sectional view of one embodiment of acirculation pump in accordance with the invention;

FIG. 2 shows schematically a partial view of a rotor and a stator andthe effective forces;

FIG. 3 shows a partial sectional view of one embodiment of a bearing formounting the rotor;

FIG. 4 shows a plan view of a first embodiment of a return-path body inaccordance with the invention;

FIG. 5 shows a perspective partial view of the return-path bodyaccording to FIG. 4 with accommodated windings;

FIG. 6 shows a variation of the embodiment according to FIG. 5;

FIG. 7 shows a perspective partial view of a second embodiment of areturn-path body in accordance with the invention;

FIG. 8 shows a perspective partial sectional view of a third embodimentof a return-path body in accordance with the invention;

FIG. 9 shows a partial sectional view of a fourth embodiment of areturn-path body in accordance with the invention;

FIG. 10 shows a partial plan view of a fifth embodiment of a return-pathbody in accordance with the invention;

FIG. 11 shows a sectional view along line 11-11 according to FIG. 10;

FIG. 12 shows a lateral sectional view of a sixth embodiment of areturn-path body in accordance with the invention;

FIG. 13 shows a sectional view along line 13-13 according to FIG. 12;

FIG. 14 shows a lateral sectional view of a seventh embodiment of areturn-path body in accordance with the invention;

FIG. 15 shows a plan view of the return-path body according to FIG. 14;

FIG. 16 shows a lateral sectional view of an eighth embodiment of areturn-path body in accordance with the invention;

FIG. 17 shows a plan view of the return-path body according to FIG. 16;

FIG. 18 shows a schematic side view of one embodiment of a return-pathbody element; and

FIG. 19 shows an embodiment of a toroidal winding on a return-path body.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of an inventive electric motor which is designated inFIG. 1 as a whole by reference numeral 100 is part of a circulation pump102 so that a pump-motor unit is formed. The circulation pump 102comprises a housing 104, in which the electric motor 100 is arranged.The circulation pump 102 is, as described in greater detail below,designed as a centrifugal pump.

The electric motor 100 has a rotor 106. An impeller 108 is non-rotatablyconnected to the rotor 106 in order to form a rotor-impeller unit.

The electric motor 100 comprises, in addition, a stator 110 with one ormore windings and a return-path body 114, for example, in the form of asoft magnetic return-path ring in one piece or several pieces.Embodiments according to the invention of return-path bodies aredescribed in detail below. The stator 110 is arranged non-rotatably inthe housing 104.

The rotor 106 is designed in one embodiment so as to generate a magneticfield. For this purpose, it comprises one or more magnetic elements 116,which are, in particular, permanent magnets which are magnetized in aradial direction. The magnetic elements 116 may be formed via permanentmagnets of a high coercive field strength, wherein the magnetic poles ofthe individual magnetic elements are arranged over the circumference ofthe rotor 106 with alternating poles.

A surface 118 of the rotor 106 facing the stator 110 is part of asubstantially spherical surface, wherein the magnetic elements 116follow this surface configuration. In order to protect the magneticelements 116, the rotor 106 has a casing 120 which may be produced fromplastic or high-grade steel which forms the surface 118.

The spherical surface 118 corresponds to a section of an imaginarysphere which has been cut at right angles to an axis 122 (FIG. 2) whichextends through the center point of the imaginary sphere. An area 124 ofthe rotor 106 facing the housing 104 has, as a result, an essentiallyflat surface. The same applies for an area 126 of the rotor 106 whichpoints towards the impeller 108.

An air gap 128 for the magnetic return path is formed between the rotor106 and the stator 110 and, in particular, its return-path body 114. Awall 132 arranged in the air gap 128 acts as a partition wall to the wetarea of the circulation pump 102 in order to protect the return-pathbody 114 with the windings.

The rotor 106 is mounted spherically in order to form a centrifugalpump. A corresponding bearing 136 comprises a sliding member 138 whichis designed as a sphere and is seated on a support column 134 (FIG. 2).This support column is arranged so as to be non-rotatable in the housing104. The center point of the sliding member 138 is seated substantiallyon the axis 122 of the rotor. Furthermore, the center point of thesliding member 138 coincides substantially with the center point of theimaginary sphere which forms the surface 118.

The bearing 136 comprises, in addition, a bearing cap 140 (FIG. 3) whichis produced, for example, from carbon. The sliding member 138, which maybe produced from a hard material and, in particular, a ceramic material,can slide in the bearing cap 140 relative to the bearing cap 140. Thebearing cap 140 is connected non-rotatably to the rotor 106. As aresult, to a great extent, mounting of the rotor 106 in the housing 104free of play can be realized.

The bearing cap 140 comprises, as shown in FIG. 3, a hollow cylindricalsection 142 with a diameter D which corresponds essentially to aspherical diameter d of the sliding member 138. An air gap 146 is formedbetween the sphere 138 and a bearing cap wall 144, the extension of thisair gap transversely to the axis 122 being considerably smaller than thediameter d of the sliding member 138.

A spherical section 148 follows the hollow cylindrical section 142 inaxial direction (in the direction of the axis 122), wherein the centerpoint of the imaginary sphere forming this spherical section coincideswith the center point of the sliding member 138 which is a slidingsphere for the bearing 136. The radius R of this imaginary sphere, whichforms the spherical section 148, corresponds to the radius d/2 of thesphere of the sliding member 138.

A central, material-free area 150 is formed in the bearing cap 140 aboutthe axis 122 of the rotor 106. This area is, therefore, arranged in thespherical section 148 and is connected via the spherical section 148 tothe hollow cylindrical section 142. This central, material-free area 150is of a symmetric design in relation to the axis 122 and has a diameterM.

The central, material-free area 150 forms a lubricating bore, via whicha lubricating medium, such as a liquid being conveyed, may be suppliedto a sliding surface 152 of the sliding member 138 and to a slidingsurface 154 of the bearing cap 140, in particular, at the sphericalsection 148.

The sliding member 138, which is seated on the support column 134, dipsinto the hollow cylindrical section 142 of the bearing cap 140 and canslide over the spherical section 148 relative to the bearing cap 140.Axial and radial forces of the rotor 106 may be transferred to thesliding member 138 via the spherical section 148. The sliding member 138accordingly exerts a counterforce on the rotor 106 and, therefore, onthe bearing cap 140.

In one embodiment of the electric motor, the rotor 106 generates amagnetic field via the magnetic elements 116, i.e., the magnetic fieldproceeds from the rotor 106. In the air gap 128, lines of forces extendbetween the rotor 106 and the soft magnetic return-path body 114 of thestator 110. In this respect, they do not, however, extend parallel butrather have a relatively large curvature. As a consequence, largedifferences in radial force occur when the rotor 106 becomes displacedoff-center with respect to the stator 110. For example, when an axis 158of the stator 110 and the axis 122 of the rotor 106 no longer coincide,one magnetic pole of the magnet 116, which is located closer to thereturn-path body 114 on account of the eccentricity, experiences agreater radial force than the magnetic pole which is locateddiametrically opposite and has a greater distance to the return-pathbody 114. During the movement out of a central position, the radialforce increases in the case of the magnetic pole moving closer to thereturn-path body 114 whereas it decreases in the case of a magnetic polelocated diametrically opposite. As a result, problems with stability canoccur with respect to the mounting.

Apart from or instead of an asymmetry between rotor 106 and stator 110on account of relative, off-center positions, asymmetries in themagnetization or non-symmetric formations of air-gap boundaries can leadto a resulting magnetic force which has a radial component.

The central, material-free area 150 sees to it that the problems and, inparticular, problems of wear and tear on account of asymmetry, such as,for example, eccentricity between the rotor 106 and the stator 110, areavoided to a great extent.

The rotor 106 experiences a force which is composed of the hydraulicforce and the resulting magnetic force. It acts with a resulting forceon the sliding member 138, the resulting counterforce 168 of which (FIG.4) is exerted by the sliding member 138 on the bearing cap 140. Theresulting counterforce 168 is the result of the hydraulic counterforce170 and the resulting magnetic counterforce 172. When the rotor 106 isarranged centrally, i.e., its axis 122 coincides with the axis 158 ofthe stator 1 10, the radial component of the resulting magneticcounterforce 172 is zero in the case of isotropic magnetization and theresulting counterforce 168 acts in the axial direction of the axis 122.

If, however, the rotor 106 is non-symmetric in relation to the stator110, for example, in that a parallel axial offset between the axes 122and 158 is present, as shown in FIG. 2, the divergent lines of forcelead in the case of a rotor 106 generating a magnetic field to the factthat a difference in radial force is present. Since, in addition, theaxial portion of the resulting magnetic counterforce 172 is relativelysmall when the rotor 106 with its magnetic elements 166 has a lowconstructional height in the axis 122, this means that the resultingcounterforce 168, as shown in FIG. 3, is no longer located in the samedirection as the hydraulic counterforce 170, i.e., on the axis 122 butrather at an angle thereto.

This would, however, mean that in the case of asymmetry between rotor106 and stator 110 the sliding member 138 presses off-center on thebearing cap 140 and the bearing cap 140 experiences a corresponding wearand tear as a result. The corresponding area of wear and tear on thebearing cap 140 is, however, not spherically symmetric. Rather, anannular channel would be formed in it which, leads to the bearing cap140 taking up a one-sided rolling movement during rotation about thesliding member 138, instead of sliding on the spherical surface of thesliding member 138 over its entire surface. This leads to an imbalance,to increased noise formation and to ever-increasing non-spherical wearand tear.

The central, material-free area 150 is arranged and designed such thatthe resulting counterforce 168 impinges on a material-free area, e.g.,on a cutaway area. This is so large that the force vector 168 impingeson liquid but not on any solid material of the bearing cap 140. As aresult, no non-spherical wear and tear of the bearing cap 140 can resulteven with angled force vectors 168 and so, to a great extent, themounting of the rotor 106 in the housing 104 free of play is ensuredover a longer period of time.

The return-path body 114 in accordance with embodiments of the inventionis produced from a compressed powder material with soft magneticproperties. As a result, a plurality of design possibilities results forthe return-path body 114 in order to optimize the operation of theelectric motor 100 and, in particular, of the circulation pump 102depending on the application.

Suitable powder materials for the production of the return-path body 114are, for example, metal powders of the company Hoganas AB, Sweden, knownunder the trade name SOMALOY 500 (SOMALOY is a registered trademark ofthe company Hoganas AB). This powder material has soft magnetic irongranules which are insulated electrically from one another. As a result,the desired soft magnetic properties result for the return-path body114, while eddy-current losses are minimized.

The return-path body 114 is of a compact design or has compactindividual elements which are connected to one another. As a result, anoptimized absorption of the magnetic field and transfer to the rotor 106may be achieved. The return-path body 114 may be designed as one partand, in particular, one piece or also be designed in several parts.

The return-path body 114 is thereby of a substantially spherical designfacing the rotor 106, having a substantially spherical surface area 202at least in segments (FIG. 4) which faces the spherical surface area 118of the rotor 106. The corresponding spheres which are envelopes of thesesurface areas 118 and 202 are located substantially concentrically(i.e., their respective center points coincide).

In a first embodiment of an inventive return-path body which is shown inFIGS. 4 to 6 and designated therein as a whole as 204, this return-pathbody 204 is designed in one piece as a ring which comprises a pluralityof segments 206 which each have a substantially spherical surface area202 facing the rotor 106.

A respective winding receiving means or coil receiving portion (coilreceiving means) 208 is formed between adjacent segments 206 in order toaccommodate a respective coil 211 with a plurality of windings (FIGS. 5,6).

The respective coil receiving portions 208 are formed by recesses 210which are set back in relation to the spherical surface area 202. Recess210, therefore, has an area 212 which is set deeper in relation to thespherical surface area 202 of the adjacent segments 206.

In the illustrated embodiment, a coil receiving portion 208 has asupport element 214, onto which the respective coil 211 can be wound orplaced. The support element 214 is provided with an electric insulation,such as, for example, a plastic layer or a plastic attachment, on whichthe coil 211 is then seated.

The coil receiving portion 208 with the recess 210 is dimensioned suchthat when a coil 211 is accommodated and, in particular, when a coil 211is wound onto the support element 214, the coil does not project beyonda spherical surface area which is formed by the enveloping surface areaof all the spherical surface areas 202 of the segments 206. As a result,the coils 211 of the return-path body 204 do not project into the airgap 128 between the rotor 106 and the return-path body 204. The air gap128 is, therefore, free from any windings.

As a result, an optimized high filling ratio may be achieved incombination with the spherical geometry of rotor 106 and return-pathbody 114 since the return-path body 114 may be arranged very close tothe rotor 106 at least in parts (with its spherical surface area). Therotor 106 is then acted upon with magnetic flux via the return-path body114 over a large surface area. In this way, very high degrees ofelectric efficiency may be realized since a considerable transport ofmagnetic flux through the air gap 128 is ensured.

The wall 132, which should be resistant to pressure and be chemicallyresistant, is arranged in the air gap 128. The air gap 128 is designedsuch that the gap in the shape of a spherical shell between thepartition wall 132 and the rotor 106 is sufficiently wide thatfrictional effects do not significantly brake the rotation of the rotor106. An optimization between friction minimization (large air gap 128)and field action on the rotor 106 (small air gap 128) may be achieveddue to the embodiments of the return-path body 114.

In the case of the illustrated embodiment of the return-path body 204,the support elements 214 are oriented in circumferential direction 216of a circle. A coil axis 218 (FIG. 5), which represents a winding axis,is, in the case of this embodiment, oriented substantially parallel tothis circumferential direction 216. The coil 211 then surrounds thesupport element 214, wherein it is in contact with this at anintermediate insulation layer or is itself provided with an insulation.The contact area with the support element 214 is an inner area 220 ofthe respective coil 211, wherein the essential portion of the magneticfield of the coil 211 is generated in this inner area 220.

Furthermore, the respective coil 211 has a contact area 222 with thereturn-path body 204, in which the respective ends of the coils abut onthe limiting walls of the recesses 210 of the segments 206, wherein anintermediate insulation layer is provided.

As a result of such a design it is possible for the return-path body 204to have (via the support element 214), in the area in which theessential part of the magnetic field is generated, a minimized crosssection which is sufficient to transport a magnetic flux below thesaturation level of the material of the return-path body, while the areatransferring magnetic flux (e.g., the sum of the spherical surface areas202 of the segments 206) has a large surface area in order to transportthe magnetic flux through the air gap 128 substantially free fromlosses.

In this way, the winding portion in the stator 110 can be minimized and,in particular, the coils 211 may be adapted to be closer to an optimizedround shape. As a result, the material required for the coils 211 isminimized. Furthermore, a high degree of electric efficiency may beachieved for the electric motor.

In one variation which is shown in FIG. 6, the number of segments 206 isincreased in comparison with the embodiment according to FIG. 5 in orderto form an electric motor with higher number of poles.

It is provided, in particular, in the case of a return-path body 204 inone piece for the coils 211 to be wound directly onto the supportelements 214 of the respective coil receiving portion 208 with anintermediate insulation layer.

It may, also be provided for the coils to be prefabricated and thenpushed onto the support elements. The coils then have a respectiveinsulation and/or the support elements are provided with the insulation.In this case, the return-path body is designed in several pieces andcomprises, as shown by way of example in FIG. 18, a plurality ofreturn-path body elements 224 which can be combined to form an annularreturn-path body. These return-path body elements 224 are, inparticular, designed such that they can be plugged into one another.

For this purpose, such a return-path body element 224 comprises a firstarea 226 which is provided with the spherical surface which ispositioned so as to face the rotor 106. The first area 226 is providedwith a prior receiving recess 232 opening to one side. A second area 228follows the first area and forms the coil receiving portion and, as aresult, is set back in comparison with the first area 226 at least inrelation to its spherical surface. This second area 228 forms, inparticular, the support element for the associated coil.

A pin element 230, which can be pushed into a recess 232 of an adjacentreturn-path body element, is seated on the second area.

A return-path body ring may be plugged together accordingly with aplurality of such return-path body elements 224. The coils,prefabricated prior to being plugged together, can be pushed onto thesecond area 228. Otherwise, the return-path body formed with return-pathbody elements 224 functions as described above. The individual segmentswith a spherical surface can be formed on the return-path body elementsor also be formed via adjacent elements.

In a second embodiment of a return-path body, which is designated inFIG. 7 as a whole as 234, coil receiving portions 236 are provided whichare provided on respective segments 238 with spherical surface areasfacing the rotor 106.

A respective recess 242 is formed between spaced segments 238 facing therotor 106 and accommodates part of a coil 244 held by the respectivecoil receiving portions 236. While in the embodiment according to FIGS.4 to 6, the coils 211 are arranged completely in the respective recesses210, in the embodiment illustrated in FIG. 7 only parts of the coils 244are arranged in the recesses 242.

The coils 244 have a coil axis which is oriented substantially withrespect to the return-path body 234. The corresponding coil axes aredirected generally towards the rotational axis 122. The coils 244 are,therefore, wound around the segments 238 or placed on them, wherein therespective segments 238, in particular, themselves have recesses, inwhich the respective coils 244 are then arranged.

In this respect, it may be provided for the return-path body 234 to havea raised outer edge 246, for example, in the shape of an edge bead sothat the coils 244 do not project beyond the upper area of thereturn-path body. This edge bead can also serve for the positioning, inparticular, in a radial direction of the coils 244.

In this embodiment, as well, the coils 244 do not project into the airgap 128.

In a third embodiment of a return-path body 248 (FIG. 8), this comprisesan annular area 250 which is arranged in the shape of a ring around therotor 106 and has a plurality of segments 251 which have sphericalsurfaces 252 facing the rotor.

A gap 253 is formed between adjacent segments 251 in order to separatethem magnetically.

The return-path body 248 comprises, in addition, a connecting part 254which makes available a return-path connection between segments 251 ofthe annular area 250 which are located opposite one another and, inparticular, located diametrically opposite one another. The connectingpart 254 has, an extension transversely to the ring axis of the annulararea 250. The number of connecting parts 254 corresponds preferably tohalf the number of segments 251. The connecting part 254 has a supportarea 256 in the form of a tooth 257 which supports the associatedsegment 206.

These teeth 257 are seated integrally on a connecting area 258 which is,for example, of a disk-like design and via which the magnetic flux canbe conducted.

The support area 256 is adapted in its shape to the annular area 250 inorder to make a secure support of the segments 251 on the connectingpart 254 possible without essentially hindering the magnetic flux. Inthis respect, it may, for example, be provided for a segment 251 to havea respective annular lip 260, with which the segment 251 can be placedover the associated tooth 257 of the support area 256.

The support area 256 is provided with recesses, in which respectivecoils 262 are arranged. Some of these recesses are formed by the gap253. An additional part is formed by a recess 259 between the teeth 257which extends radially. Coil axes of these coils 262 are orientedsubstantially parallel to the axis of rotation 122 and uniformlydistributed over the circumference of the annular support area 256 insectors.

The coils 262 are seated, beneath the annular area 250 with thespherical surfaces 252 and, therefore, do not project into the air gap128.

It is provided, in particular, for a surface of the connecting area 258facing the annular area 250 to make a contact surface available for thecoils 262 (with an intermediate insulation) in order to make an easypositioning possible.

The coils 262 may be wound onto or placed on their respective coilreceiving portions 263 at the support areas 256 before the segments 251are placed on the connecting part 254 and affixed to it. As describedabove, an insulation is provided for the electric separation betweenreturn-path body 248 and windings of the coils 262.

In a fourth embodiment of a return-path body, which is shown in FIG. 9and designated therein as a whole as 264, a segmented annular area 266with substantially spherical surface areas 268 on the segments islikewise provided. A gap is located between adjacent segments. Aconnecting part 270 connects oppositely located segments of the annulararea 266.

A flange 272, via which the segments are seated on the connecting part270, is arranged on each of the segments of the annular area 266.

A respective coil receiving portion 274 for a coil 276 is formed by theflange 272.

The flange 272 is oriented such that it is located at an angle to theaxis of rotation 122. The orientation is, in particular, such that withcoils 276 in place, the coil axes pass through the sphere center pointof the spherical surface 268.

The connecting part 278 has an inclined end face 278 in order to be ableto accommodate the respective flanges 272.

In the case of the return-path body 264, the coils 276 are seated behindthe spherical surface 268 so that a large surface area facing the rotor106 also results in this case.

In the case of the embodiments according to FIGS. 8 and 9, the magneticconnection is brought about between individual segments below the(imaginary) sphere which forms the spherical surfaces facing the rotor.

In a fifth embodiment of a return-path body, which is shown in FIGS. 10and 11 and designated as a whole as 280, this return-path body iscomposed of a plurality of separate elements 282.

A corresponding element 282 has oppositely located, outer limiting wallswhich are located in radial directions so that the element 282 islocated between them in the form of a sector. The respective elements282 each have a substantially spherical surface area 284 facing therotor 106 and thus represent a segment with a spherical surface.

A first flange part 286 and a second flange part 288 are seated to therear facing away from this spherical surface area 284, wherein the firstflange part 286 cooperates with the second flange part 288 of anadjacent element and the second flange part 288 cooperates with thefirst flange part 286 of an element adjacent on the other side.

The two flange parts 286, 288 form on adjacent elements 282 respectivecoil receiving portions 290 for coils 292 which are then seated behindthe spherical surfaces 284

The respective elements 282 have, recesses 294, in which the coils 292are at least partially arranged.

The flange parts 286 have corresponding support elements 296 which limitthe respective recesses 294 in a radial direction. The coils 292 arewound onto or placed on these support elements 296 (with intermediateinsulation layers), wherein the respective coil axes lie incircumferential direction or at least tangentially to thecircumferential direction.

A coil 292 may be placed on a support element 296, for example, of thefirst flange part 286 of an element 282. An adjacent element is thenconnected to the element 282 and, in particular, plugged into it. As aresult, the coil is also pushed onto the support element 296 of theadjacent element which is seated on its second flange part 288. Thecoils 292 are held, as a result, on coil receiving portions 290 whichextend over two elements 282, namely adjacent elements 282. The magneticreturn path is then brought about via adjacent elements 282.

The electric motor has been described on the basis of an embodiment of asynchronous rotor 106 with permanent magnets. It is also possible to usethe disclosed solution for the return-path bodies in other rotorvariations, such as cage rotors and hysteresis rotors.

It is likewise possible to design DC electric motors or AC electricmotors with the disclosed embodiments of the return-path bodies.

In a sixth embodiment of a return-path body, which is shown in FIGS. 12and 13 and designated therein as a whole as 298, the return-path bodyhas a plurality of elements 300 which, when placed together, form thereturn-path body 298. These elements 300 have a substantially sphericalsurface area 302 facing the rotor. The return-path body 298 is segmentedaccordingly. The elements 300 have, in addition, an extension beneaththis spherical area in a support area 304. This support area 304 is,therefore, arranged beneath an imaginary sphere 306 which limits thespherical surface area 302 of all the sectors 300 (e.g., forms thesurface envelope of these spherical surface areas 302).

A respective recess 308 is formed in the support area 304 in order toaccommodate, for example, one respective coil 320 per element 300 or twoelements 300. This coil receiving portions 312 thus formed comprise acarrier 314, on which the respective coil 310 is placed or directlywound (with intermediate insulation).

With a corresponding arrangement and design of the carriers 314, it ispossible for coils 310 with axes lying transversely to be positionedbeneath the spherical surface area 302 of the return-path body 298.

With a corresponding adaptation of the elements to one another, thereturn-path body 298 may be put together from these individual elements.

In a seventh embodiment of a return-path body, which is shown in FIGS.14 and 15 and designated therein as a whole as 316, this comprises asupport element 318, by means of which a coil receiving portion 320 isformed. A coil 322 with a coil axis transverse to the axis of rotationof the rotor and, in particular, at substantially right angles theretois seated on this support element 318, wherein the coil 322 is seatedcentrally. An axis of symmetry of the coil 322 (mirror axis), which isat right angles to the coil axis, coincides with the axis of rotation.

Return-path body segments 324, which each have a substantially sphericalsurface area 326, are seated on the support element 318.

For example, four segments 324 are provided, wherein two oppositelylocated segments are connected by the support element 318 in the mannerof a web.

The two other oppositely located segments are connected via anadditional support element 328, wherein this additional support element328 projects beyond a side surface 330 of the return-path body 316. Thesupport element 328 is, for example, of a U-shaped configuration.

A coil receiving portion 332 is likewise formed on the support element328, wherein a recess 336 for the partial accommodation of a coil 338 isformed between oppositely located arms 334 a, 334 b. The coil 338 has acoil axis which lies transversely and, in particular, at substantiallyright angles to that of the coil 322.

The coil 338 is therefore located outside a cylindrical area whichcomprises the spherical surfaces 302 and beneath the sphere which is theenvelope of these spherical surfaces. The coil 322 is located within thecylindrical area and beneath the envelope sphere.

The return-path body 316 has a recess 340 between the oppositely locatedsegments 324 in order to form the coil receiving portion 320 foraccommodating the coil 322. The coil 322 is seated at least partially inthis recess.

In an eighth embodiment of a return-path body, which is shown in FIGS.16 and 17 and designated therein as a whole as 342, a substantiallyspherical surface area 344 is again provided which faces the rotor.

At least one coil 346, which is oriented symmetrically with respect toan axis of rotation of the rotor, is seated beneath the sphericalsurface area 344. The coil axis lies transversely and, in particular, atsubstantially right angles to this axis of rotation. A cross section ofthis coil 346 extends over essentially the entire width of thereturn-path body 342.

This comprises, a support element 348, onto which the coil 346 is woundor placed. The support element 348 is part of a coil receiving portion350 which also comprises a recess 352 in the return-path body 342, inwhich the coil 346 is partially accommodated.

Furthermore, a recess 354 is provided which extends over the width ofthe return-path body 342 so that the coil can also be positioned in itsymmetrically to the axis of rotation over the width of the return-pathbody. In the case of a two-pole configuration, two coils are providedand the coil axes of the coils lie transversely and, in particular, atsubstantially right angles to one another.

If the return-path body is produced with a compressed powder material,many possibilities result with respect to the selection of geometry.Three-dimensional, defined shapes may, in particular, be realized. Whena spherical surface 202, which faces the rotor 106, is formed at leastin segments, the air gap 128 may be minimized, wherein the transferringarea with respect to the magnetic flux may be configured with asufficiently large surface area. Furthermore, the winding portion(“copper portion”) on the stator 110 may be minimized since the coilreceiving portion can be optimized for accommodating the windings. Highdegrees of efficiency then result with low material use.

It may also be provided for a return-path body 356 (FIG. 19) to beformed in one piece in a ring shape with a spherical surface area 358which faces the rotor.

In this embodiment, several separate coils 360 are wound onto thisreturn-path body 356 and are toroidal in shape. These coils 360 arethereby adapted to the shape of the annular return-path body 356. Theircoil axis lies in circumferential direction, wherein the coil axis iscurved and, generally, part of a circle. The return-path body 356 as awhole therefore forms the coil receiving portions.

A coil 360 is seated on the return-path body 356 such that its windings362 abut on it. An outer side 364 of the return-path body 356 has acylindrical surface. The windings 362 are guided so as to abut betweenthis cylindrical surface and the spherical surface 358. The area oftransition is formed by annular end faces 366, 368.

The windings lie, for example, at an angle to an axis of the return-pathbody 356 in order to make the abutment possible. The individual windings362 can, in particular, be formed from a flat material in order toachieve a coil which follows the contour of the return-path body 356 inan optimum manner.

In the case of this embodiment, coil parts are located in the air gap128, wherein the proportion of the entire coil portion can, however, beminimized.

While particular embodiments of the present invention have beendisclosed, it is to be understood that various different modificationsand combinations are possible and are contemplated within the truespirit and scope of the appended claims. There is no intention,therefore, of limitations to the exact abstract and disclosure hereinpresented.

1. An electric motor comprising: a rotor; and a stator; wherein therotor is supported on a substantially spherical bearing and is of asubstantially spherical design facing the stator; wherein the stator hasa magnetic return-path body made of a compressed powder material; andwherein the return-path body comprises a plurality of segments eachhaving a substantially spherical surface facing the stator; and whereinthe return-path body has coil receiving portions which are arrangedunder the spherical surface areas facing the stator.
 2. The electricmotor according to claim 1, wherein: the return-path body is a compactbody or comprises compact return-path body elements.
 3. The electricmotor according to claim 1, wherein: the return-path body is composed ofa plurality of return-path body elements.
 4. The electric motoraccording to claim 3, wherein: adjacent return-path body elements areconnected via a plug connection.
 5. The electric motor according toclaim 1, wherein: adjacent segments are magnetically separated.
 6. Theelectric motor according to claim 1, wherein: a gap is provided betweenadjacent segments.
 7. The electric motor according to claim 1, wherein:segments are connected to one another via a return-path area.
 8. Theelectric motor according to claim 1, wherein: the return-path bodysurrounds the rotor in a ring shape.
 9. The electric motor according toclaim 1, wherein: the powder material comprises iron granuleselectrically insulated relative to one another.
 10. The electric motoraccording to claim 1, wherein: the coil receiving portion is providedwith an electric insulation and/or an accommodated coil is provided withan electric insulation towards the coil receiving portion.
 11. Theelectric motor according to claim 1, wherein: the coil receivingportions are arranged and designed such that accommodated coils do notproject beyond the spherical area of the return-path body in thedirection of the rotor.
 12. The electric motor according to claim 1,wherein: an air gap formed between the rotor and a spherical area of thereturn-path body is free from coils.
 13. The electric motor according toclaim 1, wherein: the return-path body has a plurality of recesses ascoil receiving portions or for the formation of coil receiving portions.14. The electric motor according to claim 13, wherein: a recess havingan area facing the rotor is set back in relation to the sphericalsurface of the return-path body.
 15. The electric motor according toclaim 1, wherein: a coil is wound onto a coil receiving portion.
 16. Theelectric motor according to claim 1, wherein: a prefabricated coil ispositioned onto a coil receiving portion.
 17. The electric motoraccording to claim 1, wherein: a coil receiving portion is dimensionedsuch that the part of the return-path body located in the area of thegenerated magnetic field of the accommodated coil is considerablysmaller than the area of the return-path body transferring the generatedmagnetic field towards the rotor.
 18. The electric motor according toclaim 1, wherein: a coil receiving portion is dimensioned such that anadequate area of the return-path body is made available in order totransport magnetic flux below the saturation level.
 19. The electricmotor according to claim 1, wherein: a coil receiving portion isdesigned such that a coil with a round or approximately round crosssection is adapted to be accommodated.
 20. The electric motor accordingto claim 1, wherein: the coil receiving portions are arranged behind orbeneath the spherical surface area of the return-path body facing therotor.
 21. The electric motor according to claim 20, wherein: thereturn-path body has a connecting area located transversely to an axisof rotation of the rotor and making a transverse magnetic connectionavailable.
 22. The electric motor according to claim 21, wherein: thecoil receiving portions are formed at the connecting area.
 23. Theelectric motor according to claim 1, wherein: the rotor is a cage rotor.24. The electric motor according to claim 1, wherein: the rotor isadapted to generate a magnetic field.
 25. The electric motor accordingto claim 24, wherein: the rotor comprises a plurality of permanentmagnets.
 26. The electric motor according to claim 1, wherein: the rotoris a hysteresis rotor.